Over the past decades numerous optochemical sensors and biosensors have been developed for the measurement and continuous monitoring of important physical, chemical and biological parameters. Corresponding sensing materials often rely on indicator dyes incorporated in polymeric matrices, which provide means for qualitative or quantitative assessment of analyte(s) of interest by measuring sensor optical properties. Such materials are routinely used for sensing of: gaseous specie such as oxygen, carbon dioxide, ammonia, sulfur dioxide, organic vapors; ionic specie such as pH, Na+, K+, Ca2+, NH4+, NO3−, NO2−, organic molecules and metabolites; other bio- and macromolecules, in conjunction with absorbance, reflectance, fluorescence/phosphorescence, or chemiluminescence detection in the UV-VIS range. Polymeric sensors are commonly used, especially for gaseous analytes and small molecules (e.g. ions) (O. S. Wolfbeis (ed.), Fiber Optic Chemical Sensors and Biosensors, CRC Press, Boca Raton, Fla., 1991, v.1,2). This methodology allows production of sensor elements on both small and large scale using rather simple procedures and equipment.
Molecular oxygen (O2) is the analyte of major importance, and optical oxygen sensors have been investigated for many years. O2 is a quencher of long-decay fluorescent and phosphorescent dyes, so it can be ‘sensed’ directly by luminescence quenching (Papkovsky D. B., Methods in optical oxygen sensing: protocols and critical analyses, In: Methods Enzymol. 2004, v.383, p. 715-734). For such O2-sensitive materials, both luminescence intensity and decay time of the dye are reduced in the presence of O2, thus allowing quantification, by intensity or lifetime measurements or by phase-fluorometry. Lifetime based sensing of O2 realised by the latter two methods is advantageous for many applications.
O2 sensors are usually prepared in the form of a solid-state material (coating, film, membrane—see e.g. U.S. Pat. Nos. 4,003,707 and 5,718,842), a soluble reagent (probe—see e.g. U.S. Pat. No. 5,837,865 and WO2008012785-A2), a dispersed matter (nano- and micro-particles dopped with indicator dye—see e.g. Borisov, S M, Mayr, T, Klimant, I—Anal Chem, 2008, v.80, p. 573-582), or combinations thereof (e.g. WO2002103334 Klimant I, Krause C). The solid-state sensor approach allows easy manipulation and reuse of sensors, and avoids sample contamination.
To produce a solid-state active element, an O2-sensitive dye is usually embedded in a suitable matrix which provides the desired quenchability and response characteristics (sensitivity, response time, etc.). By selecting the dye, the medium and encapsulation process, one can optimise photophyscial and sensing characteristics for accurate measurement of O2 concentration. Examples of O2-sensitive materials are: pyrene butyrate in silicone rubber (U.S. Pat. No. 4,003,707), Ru-tris(bipirydyl) dye in silicone rubber (U.S. Pat. No. 5,030,420), Ru(dpp)3 dye incorporated in sol-gel matrix—ormosil (US 20060257094; Klimant), Pt-octaethylporphin-ketone dye in polystyrene (U.S. Pat. No. 5,718,842), Pt-tetrakis-(pentafluorophenyl)porphine in a polymer (U.S. Pat. No. 4,810,655 and U.S. Pat. No. 6,653,148).
Fabrication procedures for such sensors usually involve preparation of sensor components in an appropriate solvent (i.e. ‘coating cocktail’) which is applied on a suitable solid support. After drying, polymerisation or curing, solid-state polymeric composite is formed. Preparation of such thin film O2-sensitive coatings may be achieved by casting, spin-coating, dip-coating, tampon or jet printing, co-polymerization, of such cocktails. Such thin film coatings usually require a special support material to maintain their integrity and stability during operation and handling. However, the need for sensor support leads to a problem of adhesion of sensor composite to it. Strong interaction between the two materials is not desirable as this may lead to the formation of mixed phases and/or regions of heterogeneity, thus affecting sensing properties. Common matrices used in O2 sensors (hydrophobic polymers such as polystyrene) are not very compatible with support materials such as glass or other polymers (e.g. polyethylene and polypropylene widely used in packaging). The use of microporous support materials coated with the polymeric O2-sensitive compositions has been described (Papkovsky D. B. et al. Sens. Actuat. Part B., 1998, v.51, N1-3, p. 137-145). Sensors are prepared in the form of membranes, sheets, inserts, coated fibres, sensor arrays (e.g. coated microplates).
Therefore, fabrication of traditional O2 sensors generally requires the following components: indicator dye, encapsulation medium, support material and solvent. Some additives required for sensor operation (plasticiser) can also be incorporated. The use of such complex cocktails containing polymer and volatile solvents complicates production of sensors and imposes certain restrictions. Thus, viscous and volatile formulations are difficult to handle, manipulate and dispense in small volumes, they tend to dry during casting procedure or printing. Also thin film coatings are fragile, tend to degrade with time, delaminate and fall off, especially from hydrophobic and flexible support materials. Although traditional sensor design and fabrication techniques produce satisfactory sensors, they are relatively complex from the fabrication point of view and not very suitable for certain applications where high accuracy and reproducibility of measurements is required (e.g. with disposable or calibration free sensors). Complex composition and fabrication of the current O2 sensors, non-optimal physical-chemical and sensing properties, limited applicability and analytical performance and relatively high production costs limit their use. Incorporation of such sensors in sample vessels or packages made of inert materials is also difficult and requires additional steps and components (e.g. adhesive). The development of more simple, robust and materials having superior sensing properties is therefore highly needed.
The invention addresses at least one of these issues by providing new materials and fabrication processes which enable advanced sensing systems, and also uses of such sensors in a number of high-utility applications such as packaging, biopharmaceutical, biomedical. It also demonstrates that this approach is applicable to a range of different sensing systems and materials, primarily to fluorescence/phosphorescence based sensors for O2, enzyme biosensors on their basis, but also to other indicator-mediated sensors for pH, CO2 and some other important analytes.